Far better than some of these band-aid solutions is to focus on the underlying economics of the problem and remedy those. Giving the end purchasers (aka students) and not the professors (aka middle-men) the power to choose books will drastically help to level the playing field. I’ve written some more specific thoughts and hints here: “To Purchase, Rent, or Pirate? The Broken Economics of Textbooks in the Digital Age” http://boffosocko.com/2015/08/24/to-purchase-rent-or-pirate-the-broken-economics-of-textbooks-in-the-digital-age/